1. Field of the Invention
The present invention relates to a toner replenishing device for replenishing a toner to a developer storing container of a developing section for developing an electrostatic latent image using a two-component developer composed of a toner and a carrier, as well as an image forming apparatus having the same.
2. Description of the Related Art
Electrophotographic image forming apparatuses for forming an image utilizing an electrophotographic process are used, for example, as copying machines, printers, or facsimile machines. The electrophotographic image forming apparatus includes a photoreceptor drum, a charging device, an exposing device, a developing device, a transfer device, and a fixing device.
In the image forming apparatus described above, the exposing device exposes a photosensitive surface of the photoreceptor drum charged by the charging device to form an electrostatic latent image. Then, in the developing device, the formed electrostatic latent image is developed using a two-component developer composed of a toner and a carrier, and thereby a toner image as a visible image is formed. The toner image is transferred onto a recording material such as paper by the transfer device, and then the transferred image is fixed by the fixing device, and thereby an image is formed.
As described above, in the image forming apparatus for developing the electrostatic latent image using the two-component developer, a concentration of the toner contained in the two-component developer affects quality of a formed image. Therefore, the image forming apparatus described above replenishes the toner to the developer storing container, and controls so that the toner concentration falls within an appropriate range, in order to obtain an image having a constant concentration.
Techniques according to the related art with respect to replenishment of a toner to a developer storing container are disclosed in Japanese Unexamined Patent Publication JP-A 6-175500 (1994), Japanese Unexamined Patent Publication JP-A 5-27596 (1993), and Japanese Unexamined Patent Publication JP-A 2006-171023. In the image forming apparatus disclosed in JP-A 6-175500, consumption of a developer with respect to each pixel of an inputted image data is estimated based on a detection result of an edge at each pixel, and replenishment of the developer is controlled based on the estimated consumption of the developer.
Further, the image forming apparatus disclosed in JP-A 5-27596 comprises a first developer concentration control device for allowing a toner replenishing section to operate to replenish a toner according to image density information of an image information signal; and a second developer concentration control device for detecting apparent permeability (hereinafter, may be referred to as merely “permeability”) of a two-component developer, and allowing the toner replenishing section to operate to replenish the toner based on the detection result. In the image forming apparatus, after a time has elapsed until the permeability of the two-component developer becomes stable, a toner replenishment control operation is switched from the operation by the first developer concentration control device to the operation by the second developer concentration control device.
Further, the image forming apparatus disclosed in JP-A 2006-171023 calculates a toner consumption based on an image data in association with development of an image corresponding to the image data, calculates corrected consumption by multiplying the calculated toner consumption by a predetermined correction factor of less than 1, carries out main replenishment for replenishing a toner based on the corrected consumption while carrying out auxiliary replenishment for replenishing the toner based on a detection result of a toner concentration sensor for detecting a toner concentration in a developer storing container.
In the technique disclosed in JP-A 6-175500, a toner is replenished only based on toner consumption calculated from an image data. The toner consumption at each pixel of the image data may be different among the pixels having a common gray scale value, thereby easily producing an error in the calculated toner consumption and accumulating the error. Therefore, a replenishing amount of the toner may be different from an amount actually required. For example, the toner may be excessively replenished. When the toner has been excessively replenished as described above, there is no alternative method but to consume the toner which has been excessively replenished by carrying out development, in order to ensure the appropriate toner concentration in a developer storing container. Therefore, it is inevitable to deteriorate quality of an image developed on a recording material.
In the technique disclosed in JP-A 5-27596, the toner is replenished by the first developer concentration control device for replenishing the toner based on the image data until the permeability of the two-component developer becomes stable. Therefore, likewise with respect to the technique disclosed in JP-A 6-175500, the toner may be excessively replenished.
In the technique disclosed in JP-A 2006-171023, the main replenishment is carried out based on the corrected consumption obtained by multiplying the calculated toner consumption by the correction factor of less than 1. However, when the replenished amount of the toner is excessively decreased, it may become possibly difficult to maintain the toner concentration in the developer storing container at a level necessary for development. In the technique disclosed in JP-A 2006-171023, there is room for improvement.